Sen. Ben Sasse, R-Neb., said the QAnon conspiracy theory is "destroying the GOP from within" and called out House Minority Leader Kevin McCarthy and newly elected Republican Rep. Marjorie Taylor Greene in an op-ed Saturday.
"Until last week, many party leaders and consultants thought they could preach the Constitution while winking at QAnon," Sasse wrote in The Atlantic. "They can't. The GOP must reject conspiracy theories or be consumed by them."
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QAnon is a conspiracy theory centered on the baseless belief that President Trump is waging a secret campaign against enemies in the "deep state" and a child sex-trafficking ring run by satanic pedophiles and cannibals.
Sasse called Greene, of Georgia, "cuckoo for Cocoa Puffs" for supporting QAnon, although she's since rejected the movement. He criticized fellow Republican McCarthy for failing to "disavow her campaign."
"She once ranted that 'there’s a once-in-a-lifetime opportunity to take this global cabal of Satan-worshiping pedophiles out, and I think we have the president to do it,'" Sasse wrote. "McCarthy failed the leadership test and sat on the sidelines."
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The senator also criticized Greene's plan to file articles of impeachment against President-elect Joe Biden the day after the inauguration.
Greene responded to Sasse's op-ed during an interview with 11Alive on Sunday.
"Your viewers are people in Georgia," Greene said. 'They don't care what Sen. Ben Sasse has to say. What they care about is their election integrity. They care about their votes not being stolen, and nobody gives a flip about Ben Sasse and what he has to say. He's a never Trumper, he's a turncoat Republican and our voters could care less about what he has to say about me or anyone else."
Sasse, who has been an outspoken Trump critic, drawing the president's wrath, did not say how he'll vote on impeachment. The House voted to impeach Trump for inciting the insurrection at the Capitol on Jan. 6.
"If and when the House sends its article of impeachment against Trump to the Senate, I will be a juror in his trial, and thus what I can say in advance is limited," Sasse wrote.
"But no matter what happens in that trial, the Republican Party faces a separate reckoning. ... We can dedicate ourselves to defending the Constitution and perpetuating our best American institutions and traditions, or we can be a party of conspiracy theories, cable-news fantasies, and the ruin that comes with them."
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Fox News' Emily DeCiccio and Edmund DeMarche contributed to this report.